Pros:
Good mix of hole layouts - some holes situated behind/among clumps of trees, a couple tunnel-ish holes, holes on ridges, doglegs, one "buried" basket, etc.
Tees - they exist (they're some sort of sand/dirt combination - so they're muddy when wet, but still, there are tees...)
Signs - good signs for each hole indicating par and distance (in meters)
Relaxed - the feel of the park (at least when I was there), was very relaxed. Parents with their kids, old couples, young couples, etc.
Cons:
Biggest con = Many walking paths criss-cross the holes or are right next to a hole, and seeing as 99% of French people have no clue what disc golf is, they will not be expecting it if you have an errant throw, so be CAREFUL! I almost hit an old couple...
Cost - 4.50 Euro if during the summer season
Other Thoughts:
5 holes (2-6) were (I presume) under construction while I was there. I assume they will be replaced in different locations before the summertime. It is probably good they are doing it, because at least one of these holes played right next to playground equipment for kids
The course lies in the midst of a very large park with a great variety of other activities - beach on a lake for swimming in the summer, tennis courts, ping pong tables, soccer field that can be rented, bike/hiking/running paths, etc., etc.
I happened to be there during the winter when it was wet and dead (as the pictures I took show), but I'm sure in the summertime it would be very beautiful.
Quite easy access from Paris. A suburban train from Gare d'Est station takes about 30 minutes to get to Lagny-Thorigny stop, then a 15 minute bus ride and 15 minute walk into the park.
Conclusion - not an especially exciting course, especially compared with any truly good course in the U.S., but as disc golf is sparse in Europe - if you happen to have a spare day in Paris, it's worth it just to go just to say you've played in France.